1. Field of the Invention
The present invention relates to a white balance adjustment method for a digital image capturing device, and more particularly, to a white balance adjustment method that uses color temperature estimation.
2. Description of the Related Art
Generally, colors reflected from an object are determined by the color of the illumination source. The human visual system is able to detect and account for this kind of color change. Therefore, regardless of whether it is a sunny day, a cloudy day, an indoor scene lit with incandescent or neon light, human eyes can account for the color change and still recognize the white color of the object. However, for digital image capturing devices, white colors generated by different illumination sources are different from each other. For example, under a tungsten lamp, the captured images may be slightly yellow, while the captured images in other environments may be slightly blue or red. In order to match human vision, the digital image capturing devices must approximate the human visual system and adjust the colors according to the original light to define “white”, and display a white color that is recognizable as such by a human observer. The above process is called a “white balance” procedure.
There are several prior art white balance adjustment methods. One is U.S. Pat. No. 6,798,449, issued on Sep. 28, 2004, which uses an R value, a G value, and a B value to obtain the average brightness and Cb-Cr values. However, if an imaged picture lacks one of the primary colors, or has a low proportion of one of the primary colors, the image will suffer from aliasing. Another prior art technology uses the brightest spot in an image for the white balance adjustment process; however, if the brightest spot in the image is not a white spot, the adjusted image will not provide the best possible picture.
Another prior art technology marks a plurality of color temperatures on a G/B-G/R coordinate graph, extracts grey points from a desired image, and converts them onto the G/B-G/R coordinate graph to determine the proper color temperature for the image. However, if the picture has a lot of background colors, or the correct color temperatures are not near the marked color temperature, the adjusted picture will still have a color difference.
Therefore, it is desirable to provide a white balance adjustment method for a digital image capturing device to mitigate and/or obviate the aforementioned problems.